机械合金化对Cr-W粉末及烧结材料组织的影响

通过机械球磨法制备原子比为4:1的Cr-W预合金粉末,对球磨后的Cr-W粉末进行XRD、SEM、TEM分析,探讨球磨时间对Cr-W粉末形貌、晶粒大小、组织结构及烧结Cr-W合金固溶度的影响。结果表明：采用机械合金化法,可以制备纳米级的Cr-W预合金粉末;球磨初期,晶粒尺寸、微应变变化较大,48 h后趋于稳定获得小于30 nm的纳米晶粉末;经72 h球磨后,粉末中有固溶体形成;球磨过程伴随着晶格常数的变化;球磨时间越长的粉末,烧结后各相分布越均匀,固溶程度越高     

Preparation of Aluminum Coatings Containing Homogenous Nanocrystalline Microstructures Using the Cold Spray Process

Nanostructured materials are of widespread interest because of the unique properties they offer. Well-proven techniques, such as ball milling, exist for preparing powders with nanocrystalline microstructures. Nevertheless, consolidation of nanocrystalline powders is challenging and presents an obstacle to the use of nanocrystalline metals. This work demonstrates that nanocrystalline aluminum powders can be consolidated using the cold spray process. Furthermore, transmission electron microscopy (TEM) analysis of the nanocrystalline cold spray coatings reveals that the cold spray process can cause significant grain refinement. Inert gas atomized 6061 and 5083 aluminum powders were ball milled in liquid nitrogen resulting in micron-sized powder containing 250-400 nm grains. Cold spray coatings prepared using these feed stock materials exhibited homogenous microstructures with grain sizes of 30-50 nm. TEM images of the as-received powders, ball-milled powders, and cold spray coatings are shown.     

机械合金化过程中Fe50Als50二元系的结构演变

利用高能球磨和后续热处理技术制备纳米晶Fe5A150（摩尔分数，％）合金粉体。采用X射线衍射、透射电镜和扫描电镜对元素混合粉在机械合金化过程中的结构演变及热处理对合金化粉体结构的影响等进行分析，讨论其机械合金化合成机制。结果表明：球磨过程中Al向Fe中扩散，形成Fe（A1）固溶体。机械合金化合成Fe（Al）遵循连续扩散混合机制；球磨30h后，粉体主要由纳米晶Fe（A1）构成，晶粒尺寸5．65nm；热处理导致Fe（A1）纳米晶粉体有序度提高，转变为有序的B2型FeAl金属间化合物，粉体的晶粒尺寸增大，但仍在纳米尺度范围。     

Study of the milling parameters optimization in the direct carburization of WO3 by mechanical alloying

The mechanical alloying method allows obtaining tungsten carbide by direct carburization of tungsten trioxide. The parameters that have a determining role on the kinetic reactions are the temperature and the pressure of the process. The milling installation must maintain a low pressure by removing the carbon dioxide released during the carburizing reaction.In a planetary balls mill, the energy developed during a ball impact was determined via a simplified computational modeling and depends on the mass of balls and on the speed of balls reached during the milling process. The energy dissipated during impact increases exponentially with the speed rotation of the mill and with the balls diameter.Tests were carried out in a planetary balls mill equipped with bowls lined with tungsten carbide and filled with tungsten carbide balls of 10- and 12-mm diameter. Two levels of filling of the bowls, 150 g and 200 g of balls were also tested. The balls/milled powder ratio was kept at 10:1 in all tests. To monitor the carburizing reaction, samples were taken every 3 h of grinding. They have been investigated by X-ray diffraction to determine the phases in presence. The morphology of the particles was studied by scanning electron microscopy and the particle size was investigated by laser granulometry in liquid medium.To determine the effect of various milling parameters on the temperature during a milling cycle, a temperature-monitoring device was created and installed on the grinding bowl. The obtained values demonstrate that the diameter of the balls and the filling degree of the bowl have an important role in the evolution of the temperature during milling.     

高能球磨制备Al-Pb-Si-Sn-Cu纳米晶粉末的特性

通过机械合金化制备了Al-15％Pb-4％Si-1％Sn-1．5％Cu(质量分数)纳米晶粉末。采用X射线衍射(XRD)，扫描电镜(SEM)和透射电镜(TEM)对不同球磨时间的混合粉末的组织结构、晶粒大小、微观形貌以及颗粒中化学成分分布情况进行了研究。结果表明混合粉末经过球磨后形成了纳米晶，其组织非常均匀。球磨对Pb的作用效果明显大于对Al的作用效果，经过40h球磨后Pb粒子达到40nm，而Al在球磨60h后晶粒为65nm；经球磨后，Cu和Si固溶于Al的晶格中，而Sn则固溶于Pb晶格中，并且Al和Pb发生了互溶，形成了Pb(Al）超饱和固溶体；在球磨过程中硬度高的脆性粒子Si难于完全实现合金化。     

Synthesis of (Mo1−x–Crx)Si2 nanostructured powders via mechanical alloying and following heat treatment

MoSi₂–CrSi₂ nanocomposite powder was successfully synthesized by ball milling of Mo, Si and Cr elemental powders. Effects of the Cr content, milling time and annealing temperature were studied. X-ray diffraction (XRD) was used to characterize the milled and annealed powders. The morphological and microstructural evolutions were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). High temperature polymorph (HTP) of MoSi₂ begins to form after 50 h of milling and completes after 70 h of milling. MoSi₂–CrSi₂ composite powder was also prepared with a combination of short milling time (50 h) and low temperature annealing (850 °C). Annealing led to the HTP to low temperature polymorph (LTP) transformation of MoSi₂. MoSi₂–CrSi₂ nanocomposite powder with the mean grain size less than 50 nm was obtained at the end of milling. This composite maintained its nanocrystalline nature after annealing. A spherical morphology was procured for 50 h milled powder with 0.25 mole Cr.     

Softening behaviour of nanostructured Al–14 wt% Zn alloy during mechanical alloying

Al and Zn elemental powder mixtures were subjected to high-energy milling to produce Al–14 wt% Zn alloy. The milled powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness measurement. The Al and Zn grain sizes were estimated from broadening of XRD peaks using Williamson–Hall formula. The results showed that in early stage of milling the solubility of Zn in Al is extended compared to the equilibrium value which is accompanied by a decrease in lattice parameter of the Al matrix. However, after longer milling times, decomposition of Al(Zn) supersaturated solid solution appeared to occur leading to an increase in Al lattice parameter and also a decrease in hardness value of as-milled powder. The final product of milling includes both Al and Zn phases having a grain size of 40 nm and 20 nm, respectively.     

中颗粒钨粉高温碳化制取粗晶碳化钨粉的研制

本文叙述采用中颗粒钨粉高温碳化制取粗晶WC粉的过程,探讨碳化和球磨破碎工艺对WC的性能影响,并对用中颗粒钨粉高温碳化制取的粗晶WC粉与传统工艺制取的粗晶WC粉生产的合金性能进行比较。     

纳米晶W粉和W-Ni-Fe预合金粉的制备

采用高能球磨法制备纳米晶W粉和W-Ni-Fe预合金粉，研究了不同的球磨材质包括硬质合金球(CCB)、钨球(TAB)和球磨转速、球料比及球磨时间等条件对球磨后粉末性能的影响。利用XRD，TEM和EDX分析球磨后粉末的晶粒尺寸、晶格畸变、形貌、结构变化及颗粒成分变化。结果表明：高能球磨法可制得10nm～80nm的W粉和W-Ni-Fe预合金粉，纳米级颗粒含量达80％以上。相同材质的钨球制得的纳米粉末综合性能较好。球磨过程中，粉末保持颗粒状结构，纳米级粉末颗粒形状最终趋于等轴化。     

PREPARING NANO-CRYSTALLINE La DOPED WC/Co POWDER BY HIGH ENERGY BALL MILLING

The La doped WC/Co powder was prepared by high energy ball milling. The changes of crystal structure, micrograph and defect of the powder were investigated by means of XRD (X-ray diffraction), SEM (scanning electron microscope) and DTA (differential thermal analysis). The results show that adding trace La element into carbides is effective to minish the grain size of WC/Co powder. The La doped carbides powder with grain size of 30nm can be obtained after 10h ball milling. The XRD peak of Co phase disappeared after 20h ball milling, which indicated solid solution (or secondary solid solution) of Co phase in WC phase. The La doped powder with grain size of 10nm is obtained after 30h ball milling. A peak of heat release at the temperature of 470℃ was emerged in DTA curve within the range of heating temperature, which showed that the crystal structure relaxation of the powder appeared in the process of high energy ball milling. After consolidated the La doped WC/Co alloy by high energy ball milling exhibits     

机械合金化制备Ti(Al,C)复合粉末组织结构研究

目的通过原位合成技术获得Ti(Al,C)复合粉末。方法在不同球磨时间条件下,采用机械合金化方法制备Ti(Al,C)复合粉末,其中Ti粉和Al粉的摩尔比为1:1。采用扫描电子显微镜(SEM)以及X-射线衍射仪(XRD)分析球磨后粉末的显微组织结构及物相,研究不同球磨时间对制备Ti(Al,C)复合粉末物相演变、组织结构及粒子间界面结合状态的影响。结果在球磨过程中,球磨时间越长,粉体的粒径越小,当球磨时间增长到一定程度时,延展性好的Al粉颗粒发生扁平化且其表面积不断增大,使得碎化后的Ti粉颗粒不断嵌入至Al粉颗粒中,最终形成Ti(Al)固溶体。同时根据XRD分析发现,随着球磨时间的延长,Ti(Al,C)复合粉末中的Al峰逐渐减小,说明Al不断固溶到Ti中,形成了一定量的Ti(Al)固溶体。结论通过机械球磨技术在球磨一定时间后可原位合成Ti(Al)固溶体,这说明随着Ti与Al之间的相互扩散,有利于形成Ti(Al)固溶体。     

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys by ball milling and heat treatment

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys were investigated after a combination of ball milling and heat treatment. Two different sets of balls and vials made of tungsten carbide (WC) and stainless steel (STS) were used for milling the samples. Ball milling using WC balls and vials induced WC contamination, and it caused compositional changes in the matrix during heat treatment. When STS balls and vials were used, meanwhile, no peak of the second phase caused by contamination was found in the X-ray diffraction (XRD) data. In the case of the sample that completed only the milling process, the crystallite size calculated from the XRD data, 20-30 nm, agreed well with the grain size obtained from transmission electron microscopy (TEM). On the other hand, for the sample that was heat treated after milling, the strain decreased from 0.74% to 0.18%, the crystallite size increased to 70-80 nm, and the grain size grew up to the level of hundreds of nanometers. The changes in microstructure induced by the ball milling and heat treatment influenced the hydrogen storage properties, such as plateau pressure, hysteresis, and phase transformation with hydrogen absorption. Thus, the relationship between the microstructure and hydrogen storage properties can be explained.     

COMPARISON ON REFINEMENT OF IRON POWDER BY BALL MILLING ASSISTED BY DIFFERENT EXTERNAL FIELDS

The cryogenic milling and milling in conjunction with dielectric barrier discharge plasma (DBDP)have been separately set up. The combined effect of low temperature and plasma on ball milling has been investigated by examining the refinement of particle size and grain size of iron powder using scanning electron microscopy, X-ray diffraction, and small angle X-ray scattering. It was found that the mean size of iron particles could reach 104nm only after 10 hours of ball milling in conjunction with DBDP, whereas a minimum average grain size of 8.4nm was obtained by cryomilling at -20℃; however, it is difficult to refine the particle size and grain size under the same milling condition in the absence of DBDP and cryogenic temperature.     

The FeAl–30%TiC nanocomposite produced by mechanical alloying and hot-pressing consolidation

Intermetallic matrix composites reinforced with particles such as TiC have attracted a great deal of attention over the past few years. In the present study, the mechanical alloying process followed by hot-pressing consolidation was used to produce FeAl–30%TiC nanocomposite. Since the reduction of grain size to the nanometer scale improves mechanical properties of materials, this composite may be attractive for structural applications. An elemental powder mixture of Al35Fe35Ti15C15 (in at.%) was milled in a high-energy ball mill. The phase transformations in the powder during milling were studied with the use of X-ray diffraction (XRD). Transmission electron microscopy and differential scanning calorimetry were used for examining the microstructure and the thermal stability of the milling product. The results obtained show that high-energy ball milling as performed in this work leads to the formation of a bcc phase identified as the Fe(Al) solid solution and a fcc phase identified as TiC, and that both phases are nanocrystalline. Subsequently, the milled powder was sintered at 750 °C under pressure of 4 GPa. The XRD investigations of the consolidated pellet revealed that after sintering, the material remained nanocrystalline and that there were no phase changes, except for the ordering of Fe(Al), i.e. formation of FeAl intermetallic compound, during the sintering process. The average hardness of the obtained nanocomposite is 1287 HV_0.2 (12.6 GPa) and its density is 98% of the theoretical value.     

Preparing nano-crystalline rare earth doped WC/Co powder by high energy ball milling

The nano-crystalline rare earth doped WC/Co powder was prepared by high energy ball milling. The nano-crystalline powders were characterized by means of XRD (X-ray diffraction), SEM (scanning electron microscope) and DTA (differential thermal analysis). The results show that adding trace rare earth elements into carbides is effective to minish the grain size of WC/Co powder. The grain size of rare earth doped powder became two times smaller as compared with the undoped powder within ball milling times of 25–45 h. The XRD peak of Co phase disappeared after 25 h ball milling. A sharp peak of heat release at the temperature of 597 °C was emerged in DTA curve within the range of heating temperature. After consolidated the rare earth doped WC/Co alloy by high energy ball milling exhibits ultra-fine grain sizes and better mechanical properties.     

Ultramicro molybdenum nitride powder prepared using high-energy mechanochemical method

Using the specially designed mechanochemical ball-mill equipment, ultramicro molybdenum nitride powders were prepared from pure molybdenum powders in ammonia atmosphere at room temperature by high-energy ball milling. The structure and the particle size of the powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the mass ratio of grinding media to powder was 8:1, after milling for 30h the Mo2N of fcc structure was obtained, and the average particle size of the powders was around 100 nm. It is found that the chemisorption of ammonia onto the fresh molybdenum surfaces created by milling was the predominant process during solid-gas reaction, and the energy input due to introduction of highly dense grain boundaries and lattice defects offered the activation energy for the transition from Mo-N chemisorption to molybdenum nitride. In addition, the change of Mo electronic undersaturation induced by the grain refining accelerated the bonding between Mo and N. The mechanism model of whole nitriding reaction was given. During the high-energy ball milling processing, the rotational speed of milling played a critical role in determining the overall reaction speed.     

Particle properties of submicron-sized WC–12Co processed by planetary ball milling

In this study, a conventional nano-grained tungsten carbide (WC) powder was mixed with 12 wt.% of a submicron cobalt (Co) powder in a ball mill for varying milling time periods, producing a homogeneous powder mixture which can be used to sinter near-nanocrystalline cemented carbides using short-duration sintering processes. Parameters of the wet milling process were adapted in order to maximise the mixing effect on the one hand, and to avoid particle growth during the milling process on the other. Surface analysis and microscopic examination of the milled powders showed a milling-time-dependent evolution of particle size and surface roughness. X-ray diffraction (XRD) investigation indicated a decrease of the crystallite size of WC in combination with an increase in defect density, as well as a strong increase in stacking faults in the Co. The main action of the milling mechanism is the fracturing of the WC particles. Co is distributed consistently around the WC particles. The preparation method used is a useful technique to prepare homogeneous powder mixtures of WC–Co with particle sizes below 200 nm on a laboratory scale.     

The Key Role of Ball Milling Time in the Microstructure and Mechanical Property of Ni-TiC<Subscript>NP</Subscript> Composites

Titanium carbide nanoparticle-reinforced nickel-based alloys (Ni-TiC_NP composites) with ball milling time ranging from 8 to 72 h were prepared by ball milling and spark plasma sintering. Transmission electron microscopy (TEM) and scanning electron microscopy equipped with electron backscatter diffraction were used to characterize the microstructures. Their hardness and tensile properties were measured using the Vickers pyramid method and tensile tests. TEM results showed that a slight coarsening of TiC_NP occurred during the ball milling process. The grain sizes of the Ni-TiC_NP composites with various ball milling times were different, but they were all much smaller than those of the pure Ni. In all cases, the Ni-TiC_NP composites showed higher strengths and hardness values than the unreinforced pure nickel. Furthermore, the strength of the Ni-TiC_NP composites increased initially and then decreased as a function of ball milling time. The maximum strengths occurred in the 24-h ball milling sample, which presented the lowest average grain size. The Hall-Petch strengthening was suggested to be the main reason responsible for such variations in mechanical properties. Additionally, the elongation percentage of the Ni-TiC_NP composites decreased gradually with ball milling time. This may be caused by the change of microvoids in the composite as the ball milling time varies, which is also related to their fracture behavior.     

The effect of zirconium addition on microstructure and properties of ball milled and hot compacted powder of Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu alloy

Elemental powders of the composition Al–12 wt% Zn–3 wt% Mg–1.5 wt% Cu with addition of 1 and 2 wt% Zr were ball milled in a planetary high-energy ball mill and then hot pressed in vacuum under 600 MPa pressure at 380 °C. The effect of ball milling and hot pressing on the microstructure was investigated by means of X-ray diffraction measurements (XRD), light microscopy, analytical and scanning transmission electron microscopy (TEM). Ball milling for 80 h leads to homogenous, highly deformed microstructure of aluminium solid solution with grain size below 100 nm. In the powder with zirconium addition, some part of the Zr atoms diffused in aluminium up to 0.3 wt% Zr. The remaining was found to form Zr-rich particles identified as face centered cubic (fcc) phase. Good quality samples without pores and cracks obtained by hot pressing composed of grains and subgrains of size below 200 nm. The particles of MgZn₂ phase were identified which were located mainly between compacted particles of milled powder. Hot pressed powder showed Vickers microhardness of about 195 HV (0.2 N) and ultimate compression strength in the range 611–658 MPa in the compression test. Addition of zirconium had no influence on the strength of the compacted powders.     

A study on mechanochemical behavior of B2O3–Al system to produce alumina-based nanocomposite

One possible route for producing the fine and homogenous distribution of hard particles in composite microstructure is the mechanochemical processing in which high-energy ball milling promotes the reaction in a mixture of reactive powders. In this study mechanochemical reaction of B₂O₃ and Al powder during ball milling was studied. The phase transformation and microstructure of powder particles during ball milling were investigated by X-ray diffractometry and scanning electron microscopy. The results showed that during ball milling the B₂O₃–Al reacted with a combustion mode producing Al₂O₃–AlB₁₂ nanocomposite. The crystallite size of Al₂O₃ and AlB₁₂ was 40 and 25 nm, respectively. This structure appeared to be stable upon annealing.